(Low) Voltage remains when circuit switched OFF!

NoddingDonkey · 1 Jan 2006

Hi,
A puzzler (for me at least!)
The lighting circuit in my bungalow insists on leaving an odd (low) voltage on the positive wire when it is switched OFF. All sockets and other circuits have no problem. When lights are switched OFF, the positive line shows a consistent, but different voltage for each room - from 6 volts on spots in the living room (and 27 on the main light), to 45 volts in the kitchen. Even odder, is that the spotlights in one room (where the main light has 21 volts when OFF), are the only ones in the house with ZERO volts when OFF.
I have checked this with ALL other circuits OFF at the main box and the problem is the same, so it is not induced voltage from another circuit. It would be a great help in avoiding ripping up the whole of the roof insulation if someone could suggest what's going on here. Is it a dodgy switch? There are three dimmers in the lounge, but the voltages are not altered by adjustment of these, so don't appear to be the cause.
I have thought about splitting the loop at 'half-way', then 'half again' to pinpoint the cause by elimination. Is that a good idea or not?
Any help appreciated.
Regards,
Mathew

andy · 1 Jan 2006

where are you measuring from?

insulation test could tell you more. whats the age of the wiring?

NoddingDonkey · 1 Jan 2006

All measured from the light sockets, by removing the bulbs. The wiring is all newer than 1987 (when the place was built) bar the spotlights added since by myself. I would normally suspect my own incompetence, but as things seem to be functional otherwise, I hope it is all wired up logically. The total current draw on the lighting loop is less than 1100 watts, which I gather is okay.
So, next step;
Check the voltages in every switch too? (which I ought to have done before posting the query - sorry)
What else, before the dreaded loft crawl?
Thanks,
Mathew

andy · 1 Jan 2006

its probably inductance.... just because there is a voltage doesnt mean it has enough power to do anything. do the lights come on?

NoddingDonkey · 1 Jan 2006

Not a hint of illumination from the lights, which is why I haven't panicked! (yet!)
INductance? Is that possible with no other circuit on, other than the problem loop itself? If it is, is it something to worry about or not at these figures?
Happy New Year BTW

andy · 1 Jan 2006

NoddingDonkey said:
Not a hint of illumination from the lights, which is why I haven't panicked! (yet!)
INductance? Is that possible with no other circuit on, other than the problem loop itself? If it is, is it something to worry about or not at these figures?
Happy New Year BTW

could be from the switch wire. probably nothin to worry about

Big_Spark · 1 Jan 2006

If your getting Inductance from a switch line, then you have a Insulation resistance problem..

Do you have dimmer switches on the lighting at all? These can cause a leakage on occasion..

Personally I would suggest you call in a spark to investigate, it may be nothing to worry about..but this is not the answer..you have unaccounted for voltage on a disconnected circuit..that needs to be sorted out..It could be a prelude to a bigger problem.

NoddingDonkey · 1 Jan 2006

Thanks for the help guys.
Point taken about the inductance issue and it does bug me that something is amiss, somewhere. Would you suggest splitting the loop as I had though about, to narrow down the problem, or is there a better approach? (perhaps disconnecting individual switches, one by one? If all fails with my hands, then I'll get a pro in for a look of course, but it'd be nice to sort it myself.

NoddingDonkey · 1 Jan 2006

Yes, there are dimmers in the lounge, I'll start with those.

andy · 1 Jan 2006

NoddingDonkey said:
Thanks for the help guys.
Point taken about the inductance issue and it does bug me that something is amiss, somewhere. Would you suggest splitting the loop as I had though about, to narrow down the problem, or is there a better approach? (perhaps disconnecting individual switches, one by one? If all fails with my hands, then I'll get a pro in for a look of course, but it'd be nice to sort it myself.

ive already said, insulation test would tell you if there is a problem with the insulation

ban-all-sheds · 2 Jan 2006

Big_Spark · 2 Jan 2006

BAS..the reason for an insulation resistance test is to ensure that the resistance has not broken down, or at least starting too, thus allowing charge to transfer from one core to another...

Stoday · 2 Jan 2006

ND said that everything was switched off. That means there's no current. If there's no current, there's no induced voltage. I.e. inductance cannot cause the observed voltage.

It's caused by capacitance.

This is fundamental electricity theory and I would have thought that any electrician would have appreciated the distinction between inductance and capacitance.

NoddingDonkey · 2 Jan 2006

Afternoon folks,
I have a friend with experience of household electrics coming over tomorrow, but to save his time, I have been looking at the problem again today, with more confusing results, mainly that some (not all) of the light sockets now show ZERO volts, whereas yesterday, they showed a variety of less than 50v. The others show the same as yesterday, as measured with a WhiteGold WG020 multimeter (my screwdrivers don't have lights on them

)
As noted, I switched all other circuits OFF at the box, and ALL the lights on the lighting loop OFF. The odd voltages remain and do not decay (over a couple of hours, at least). One change to yesterday, was a lounge spotlight off a dimmer started flickering, so I changed the dimmer for a new one and a similar problem exists. So, is it a clue, or just a bum pair of dimmers? When the dimmers were removed altogether, the residual voltages remained on some of the light sockets, so I believe not the cause.
There are no energy saving bulbs at all, but there is a transformer fed set of LV spots in the kitchen, though no difference to the problem when these are on or off. There is a LV spot within an overhead fan in the bathroom too, again no difference on or off. I plan to disconnect both of these to eliminate them later today.
Only one other discovery today. I have an outside light on a PIR sensor (normal bulb), when this is switched OFF as opposed to 'waiting to come on', there is just a two volt change in the problem voltages in SOME of the light sockets (not all). Baffled.
Apologies for the long post. I'm trying, with my lack of experience, to take on board all your comments, but some of it goes beyond me, hence my pal visiting tomorrow

I shall report further as soon as more is known.
Thank you.
Mathew

colport27 · 2 Jan 2006

When you measured these voltages, was it between Phase & Neutral or Phase & Earth?
Just out of interest can you measure between Neutral and Earth and see what readings this gives.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

(Low) Voltage remains when circuit switched OFF!

Big_Spark

Big_Spark

Similar threads